Preparation of active dried baker&#39;s yeast

ABSTRACT

An active dried baker&#39;&#39;s yeast is prepared by dividing fresh compressed yeast having a protein content of 45 to 60 percent into particles of 0.2 to 2.0 mm in size and drying the particles by passing therethrough a drying gas at a temperature of not more than 160*C in not more than 120 minutes to a dry matter content of at least 85 percent with a drying gas flow so that the particles are held within a temperature range of 20* to 50*C during drying.

United States Patent [191 Langejan 51 Oct. 22,1974

1 1 PREPARATION OF ACTIVE DRIED BAKER'S YEAST [76] lnventorf ArendLangejan, Henri Dunantlaan 21, Delft, Netherlands [22] Filed: June 14,1972 211 Appl. No.: 262,727

Related U.S. Application Data [63] Continuation of Ser. No 874,723, Nov.6, 1969,

abandoned.

[30] Foreign Application Priority Data Nov. 8, 1968 Great Britain52950/68 [52] U.S. Cl 426/18, 195/74, 195/98, 426/60, 426/62, 426/465,426/473 [51] Int. Cl. Cl2c 11/30 [58] Field of Search 99/96; 195/74, 82,97, 195/98; 426/18, 62, 465, 473, 60

[56] References Cited UNITED STATES PATENTS 1,306,569 6/1919 Whitney99/96 Klein 9 /96 X 1,643,047 9/1927 Balls 99/96 2,894,842 7/1959Mitchell et 21].. 99/96 2,919,194 12/1959 Johnston 99/96 3,394,0087/1968 Lodder et a1. 99/96 X 3,615,685 10/1971 Fontozzi et a1. 99/96FOREIGN PATENTS OR APPLICATIONS 763,926 12/1956 Great Britain PrimaryExaminer-David M. Naff Attorney, Agent, or Firm-Hammond & Littell [5 7ABSTRACT 17 Claims, N0 Drawings PREPARATION OF ACTIVE DRIED BAKER'SYEAST PRIOR APPLICATION This application is a continuation of mycopending application Ser. No. 874,723, filed Nov. 6, 1969, nowabandoned.

. STATE OF THE ART Bakers yeast is generally available as compressedyeast with a dry matter content of about 26 to 32 percent or as activedried yeast with a dry matter content of over 80 percent, generally morethan 90 percent. Compressed yeast has the disadvantage of relativelypoor keeping quality, so that in practice, this kind of yeast is only ofinterest in countries where the temperature is relatively low and/orfresh yeast is available on a substantially daily basis.

This disadvantage does not apply to active dried yeast which, due to itshigh dry matter content, is remarkably stable over a prolonged periodeven at ele vated temperatures and is therefore suitable for countrieswhere the temperatures are relatively high, e.g., tropical countries.Active dried yeast, however, has the disadvantage of a relatively lowactivity and in addition, it has to be subjected to a time-consumingrehydration in water to develop its activity before mixing it with flourfor preparing dough.

However, the drawback of a lower activity requiring larger quantities toobtain the same baking results, and consequently higher cost to thebaker using commercially available active dried yeast, must be acceptedin tropical countries in order to obtain the advantage of the betterkeeping quality. Consequenly in-non-tropical countries there issubstantially no interest in active dried yeast because of theabove-mentioned drawbacks.

The low activity of commercially available active dried yeasts incomparison with that of compressed yeast is shown in the followingtable. The gas production tests mentioned in this table are described inthe examples. The active dried yeasts are from several commercialsources and are indicated by symbols 1 to 5.

7 60mm Hg (this test procedure is referredto hereafter on dry matter,the gas production values of active dried yeast are considerably lowerthan that for compressed yeast.

Commercially available active dried yeast generally has a low proteincontent in the order of 40 to percent %N X 6.25, N determined by theKjeldahl method). Such yeasts are fairly stable and resistant to theusual slow drying processes. Experience has shown that yeasts having ahigh protein content are not suitable for preparing active dry yeast dueto the fact that large losses of activity occur during the usually slowdrying processes and moreover the product obtained is very unstable.Quick-drying processes, e.g. spray drying, can be applied to yeasts, butsuch methods also have the disadvantage that they lead to an appreciableloss of activity in the yeast. In addition, very finely di vided dustypowders are obtained which give rise to difficulties when they are mixedwith flour or when they are re-hydrated.

OBJECTS OF THE INVENTION It is an object of the invention to provide anactive THE INVENTION The active dried bakers yeast of the invention hasa 1 dry matter content of at least 85 percent by weight, a proteincontent 1% N X 6.25, as determined by the Kjeldahl method) of 45 topercent based on dry matter and an activity value of 420 to 600 whendetermined according to a test method which consists of mixing 480 mg ofthe dried yeast product in a mixer with 100 g of flour, adding 55 ml ofa solution containing 2 g of NaCl and mixing the mass for 6 minutes at28C to form a dough, placing the dough in a water bath maintained at 28Cand determining the amount of gas produced in the period from 10 to 175minutes afterthe start of mixing, expressed in ml at 28C and This tableshows that the gas production values for the commercial active. driedyeasts are only comparable to the gas production of compressed yeast ofhigh protein content (sample 6) when considerably larger amounts ofactive dried yeast are used, i.e., 930 mg of active dried yeast ascompared with 450 mg (based on dry matter) of compressed yeast. Whencarrying out gas production tests using equal amounts of yeast, based astest B The yeast of the invention has a much higher activity than theactive dried yeasts available hitherto and does not require rehydrationin order to develop its activity. The yeast of the invention preferablyhas a dry matter content of from to 96 percent by weight, a proteincontent %N X 6.25) of from 48 to 54 percent, and an activity value offrom 480 to 580 when determined according to test B. The-keeping qualityof the active dried yeast is comparable to that of the active driedyeasts which are currently commercially available.

For bread-making, the yeast of the invention can be mixed as such withthe flour and can readily be homogeneously distributed throughout thedough. A very advantageous property of the yeasts of the inventionoccurs when they are mixed with the flour and water to form the dough.The yeast particles disintegrate extensively and the yeast becomeshomogeneously distributed throughout the dough. This is a property whichmost active dried yeasts do not possess.

In order to obtain the highest activities, the yeast of the inventionpreferably contains a swelling agent and- /or a wetting agent. Suitableswelling agents, which are preferably used in amounts of from 0.5 to 5percent, advantageously l to 2 percent, based on dry matter, are methylcellulose and carboxymethyl cellulose. Suitable wetting agents, whichare preferably used in amounts of from 0.5 to 5 percent, advantageously1 to 2 percent, based on dry matter,'are esters of saturated fattyacids, such as fatty acid esters of sorbitan, e. g. sorbitanmonolaurate, monoplamitate, monostearate or mono-oleate; fatty acidesters of glycerol, e.g., glyceryl monostearate, a distearate ormonopalmitate; fatty acid esters of propylene glycol, e.g., propyleneglycol monostearate; or mixtures of two or more of the above mentionedcompounds.

The novel process of the invention forpreparing an active dried bakersyeast comprises dividing fresh compressed yeast having a protein content%N X 6.25) of 45 to 60 percent based on dry matter into particles, anddrying these particles in not more than 120 minutes to a dry mattercontent of at least 85 percent by weight by a drying gas flow forexample, using fluidized bed techniques) so that the particles are heldwithin a temperature range of from to 50C during the drying process toobtain an acitve dried yeast having an activity value of 420 to 600 whendetermined according to test method B Drying of the yeast particles ispreferably carried out at a temperature of from to C.

Preferably the drying time is less than minutes and advantageously lessthan 20 minutes. In order to keep the particles within the abovementioned temperature range, it is advantageous that the temperature ofthe drying gas flow at the end of the drying period be lower than at thebeginning thereof. At the start of the drying period, the temperature ofthe drying gas flow can be up to 160C.

In order to facilitate the drying process and to obtain a final yeastwhich is easily distributable through the dough, the compressed yeast isdivided into small particles, for example by extruding the yeast to formstrands and breaking up the strands to form particles, the particlespreferably having a cross-section in the range of 0.2 to 2 mm. Fromyeast particles of this size, a dried yeast end product is obtainedconsisting of particles having a cross-section within the range of about0.1 to 1 mm. The process according to the invention may be carried outdiscontinuously, but is especially suited to being carried outcontinuously.

The yeast used should be a strain having a good drying stability, forinstance strain 1777 described in British Pat. No. 989.247. Thecompressed yeast which is used as the starting material may be prepared,for example, by a process in which yeast is partially dehydrated bymeans of a hypotonic solution, e.g., a salt solution, and washed quicklyas described in British Pat. No. 763.926. The active dried yeast of theinvention may be packed in any of the usual containers, such as tins orplastic bags, in which the dried yeast is preferably kept under agreatly reduced pressure or in a nitrogen atmosphere. Suitable plasticmaterials are, for example, polyesters, polyamides, polyethylene,laminates of these materials or laminates with for example, aluminum.Another suitable material is regenerated cellulose, provided with alacquer layer.

In the following examples there are described several preferredembodiments to illustrate the invention. However, it should beunderstood that the invention is not intended to be limited to thespecific embodiments.

The test methods used in the Examples are described herein.

TEST A (for conventional active dried yeast) 930 mg of the active driedyeast is soaked for 10 minutes in 8 ml of water at 35C. The yeastsuspension obtained is mixed with mg of flour and 47 ml of an aqueoussolution containing 2 g of NaCl, the temperatures of flour and saltsolution being 28C. The mixture obtained is mixed for 6 minutes into adough, which is placed in a water bath adjusted to 28C. The amount ofgasproduced within the period of from 10 to 175 minutes after the start ofmixing is determined in ml at 28C and 760 mm Hg.

TEST B This test is carried out in the same way as test A, except that480 mg of active dried yeast is used instead of 930 mg.

TEST B 480 mg of active dried yeast is mixed as such with 100 g of flourin a mixer. After addition of 55 ml of an aqueous solution containing 2g of NaCl, the mass is mixed for 6 minutes at 28C. The remainingoperations are the same as those in test A.

TEST B (for compressed yeast) An amount of compressed yeastcorresponding to 450 mg of dry matter is suspended in 55 ml of asolution containing 2 of NaCl. After adding 100 g of flour, the dough isprepared by mixing for 6 minutes at 28C. The remaining operations arethe same as those in test A.

EXAMPLE I A centrifuged and washed yeast suspension of strain Ng.1777having a dry matter content of g/l was mixed with a suspension ofsorbitan monostearate (wetting agent) in water to give 1 g of sorbitanmonostearate per 100 g of dry yeast and the suspension was filtered togive a compressed yeast with a dry matter content of about 30 percent, aprotein content %N X 6.25) of 52.5 percent based on dry matter, and awetting agent content of 1 percent based on dry matter. The compressedyeast was extruded through a perforated plate having orifices of 0.6 mmdiameter. The product obtained was dried to 92 to 95 percent dry matterwith a stream of dry air passing through the mass of yeast. Thetemperature of this air varied during the drying operation; it was 60Cduring the first 6 minand consisted of particles having a length ofabout 2 5 mm and a cross-section of about 0.4 mm. The analysis of theproduct was: dry matter content, 93.4 percent; protein content N X6.25), 54.0 percent based on dry matter; phosphorus content expressed asP EXAMPLE 1V Three yeast suspensions obtained by propagating the yeastunder conditions which gave maximum activity in the fresh condition weredried in the same manner as in Example I using the same amount of thewetting agent to give active dried yeasts having the followingcharacteristics:

Protein Phosphorus based on dry matter, 3.20 percent. This product couldl0 figg be added, as such without preliminary soaking, to flour %Dry f k5 fggg, in order to prepare adough and could be completely matter drymatter dry matter Determination (ml) drsper sed 1n the dough. Gasproduction according to 937.0 49.2 302 545 B was 516 1 93.4 51.3 3.13 B564 93.2 53.2 3.18 B 556 EXAMPLE II By way of comparison, gas productiontests were EXAMPLE V made on a) a yeast of low protein content and on(b) ayeast of high protein content. Both yeasts were tested The methodof Example I Was ep a except that (I) before drying, 11) afterconventional drum drying drying was carried out so that the temperatureof the lasting about 18 hours and (III) after the fast dryingyeastdurlng drying was always about C. For this technique of the presentinvention. The results are set purpose, air at about 100C was firstblown through the forth in Table II. yeast mass and the air temperaturewas gradually low- Protein Phosphorus content Content (%NX6.25) (%P,0,,)Dry on dry on dry Determination Gas Drying Method Form Content mattermatter Test Production Yeast None Compressed 30.0 41.5 1.76 1} 423(a)(l) Conventional slow drying Granules 92.8 I 42.7 1.82 B2 (Mill)Quick drying of invention Particles 93.0 41.6 1.78 B2 398 (a)(lll) Nonecompressed 29.0 52.5 3.20 B 595 (b)(l) Conventional slow drying granules92.7 53.2 3.24 B2 (Mill) Ouick drying Particles 93.4 V 52.6 3.20 B" 516lh)(lll) of invention "(Pas production was not measured. since thegranules did not disintegrate homogeneously through the dough. From theabove results it can be seen that yeast (a)( 111) had a lower activitythan yeast tb)(lll1.

EXAMPLE III A yeast suspension having the following properties: drymatter content, 185 g/l; protein content (%N X 6.25) based on drymatter, 54.4 percent; phosphorus content expressed as P 0 based on drymatter, 3.25 percent, was propagated under such conditions that amaximum activity in the fresh condition was obtained.

This yeast was processed in the same way as in Example I using the sameamount of the wetting agent. The product obtained had the followingporperties, dry matter content, 93.0 percent; protein'content (%N X6.25) based on dry matter, 54.5 percent; phosphorus content expressed asP 0 based on dry matter, 3.26 percent; gas production according to testB 560- ml.

ered during drying. The overall drying time was 10 minutes. The analysisof the end product was: dry matter content, 92.4 percent; proteincontent (%N X 6.25) based on dry matter, 55.4 percent; phosphoruscontent expressedas P 0 based on dry matter, 3.20 percent; gasproduction according totest B 528 ml.

EXAMPLE VI The method of Example 1 was repeated except that duringdrying air at about C was first blown through the yeast mass and the airtemperature was gradully reduced during drying, care being taken thatthe temperature of the yeast was maintained below 40C. The overalldrying time was 81 minutes. The analysis of the end product was:dry'rnatter content, 93.3 percent; protein content (%N X 6.25) based ondry matter, 52.4 percent; phosphorus content expressed as P 0 based ondry matter, 3.15 percent; gas production accordingto test B 520 ml.

EXAMPLE vli' The processof Example W was repeated except that thewetting agent was a blend of glyceryl monostearate and glyceryldistearate. The analysisof the end product wasz'dry matter content N X6.25) base on dry matter, 53.2 percent; phosphorus content expressed onP based on dry matter, 3.16 percent; gas production according to test B521 ml.

EXAMPLE VIII cultivated in such a way that varying protein contents wereobtained:

ensure that the temperature of the dough was 26C. The fermentation timeswere as follows:

lst proof 30 min.

2d proof 25 min.

intermediate proof 30 min.

final proof 60 min. t 145 min.

The proofing temperature was 28 to 30C. The dough weight for each loafamounted to 890 g. After 30 minutes baking at a temperature of 250C, thefollowing TABLE 111 loaf volumes were measured.

' Phosphorus 1 5 Protein Content Content (%NX6.25) P205) Gas Loafprepared with sample A 2925 ml Dry 7 Based on Based on Production Loaprepared with sample B 3540 ml Matter Dry Matter Dry Matter Test B2 Loadprepared with sample C 3495 ml 92.4 45.9 2.81 452 93.5 47.4 2.85 473 935493 3,05 492 For these data, it may be seen that the active high progg-gg :2 tein dried yeast product (sample C) has a baking qual- 92:5 500 itycomparable to that of the compressed yeast from 93.5 56.7 g 3.19 4 whichit was prepared and far superior to fresh yeast of 481 low proteincontent.

Various modifications of the compositions and process of the inventionmay be made without departing EXAMPLE 1X from the spirit or scopethereof and it is to be under- The process of Example I was repeatedexcept that the sorbitan monostearate was replaced by 1 percent byweight of methyl cellulose which was added to the compressed yeastbefore drying. The results obtained are given in the following table.

In order to illustrate the baking quality of the yeast of the invention,comparative baking tests were carried out with a preferred form of theproduct. For these tests, the'following yeasts were used: a commerciallyavailable compressed yeast with a protein content %N X 6.25) of 46.1percent; a dry matter content of percent, and an activity of 408 (test B(sample A); a commercially available compressed yeast with a proteincontent %N X 6.25) of 52.5 percent; a dry matter content of 29.0percent; and an activity of 595 testB (sample B); and the quickly driedactive yeast of the invention of strain having a high protein content NX 6.25) of 52.6 percent; a dry matter content of 93.4 percent and anactivity of 516. (test B (sample C).

For these tests, 100 parts of flour, 53 parts of water, 2 parts of NaCland yeast were mixed together. The active dried yeast was mixed with theother components without previous soaking. 1.8 parts of the compressedyeast were used. A quantity of the active dried yeast (sample C) wasused equal to the amount of dry matter present in the compressed yeast.The mixtures thus obtained were mixed for 15 minutes, care being takento stood that the invention is to be limited only as defined in theappended claims.-

I claim:

1. A process for preparing a composition consisting essentially of anactive dried bakers yeast with a particle size of 0.1 to 1.0 mm and witha dry matter content of a least percent by weight, a protein content N X6.25) of 45 to 60 percent based on dry matter and an activity value of420 to 600 when determined by test method B consisting of the steps ofdividing a fresh compressed yeast having a protein content N X 6.25) of45 to 60 percent on dry weight basis into a mass of particles having aparticle size of 0.2 to 2.0 mm and drying the mass of particles bypassing therethrough a drying gas at a temperature of not more than 160Cin not more than 120 minutes to a dry matter content of at least 85percent by weight with a drying gas flow so that the particles are heldwithin a temperature range of from 20 to 50C to obtain a dried bakersyeast.

2. The process of claim 1 wherein the drying time is less than 50minutes.

3. The process of claim 1 wherein the drying time is less than 20minutes.

4. The process of claim 1 wherein the temperature of the drying gas flowat the end of the drying period is lower than in the beginning thereof.

5. The process of claim 1 wherein the yeast is subdivided by extrusion.

6. The process of claim 1 wherein the protein content N X 6.25) of thestarting material is 48m 54 percent on dry weight basis.

7. The process of claim 1 wherein the yeast is dried to a dry mattercontent of to percent by weight.

8. The process of claim 1 wherein the compressed yeast starting materialis mixed with at least one mem ber of the group consisting of swellingagents and wetting agents.

9. The process of claim 8 wherein the swelling agent is methyl celluloseor carboxy methyl cellulose.

10. The process of claim 8 wherein the amount of swelling agent used isfrom 1 to 2 percent based on dry matter.

11. The process of claim 8 wherein the wetting agent is selected fromthe group consisting of an ester of saturated and unsaturated fattyacids, a fatty acid ester of glycerol, a fatty acid ester of propyleneglycol and mixtures of two or more thereof.

12. The process of claim 8 wherein the amount of wetting agent used isfrom 1 to 2 percent based on dry matter.

13. The process of claim 1 wherein yeast strain Ng 1777 is used as thestarting material.

14. The process of claim 1 wherein the compressed yeast startingmaterial used is prepared by partially dehydrating with a hypotonicsolution and quickly washing the solution from the yeast.

15. The process of claim 1 wherein the drying step is carried outcontinuously.

16. In a process for making baked products from a dough containingyeast, the improvement which comprises using an active dried bakersyeast with a dry matter content of at least percent by weight, a proteincontent %N X 6.25) of 45 to 60 percent based on dry matter and anactivity value of 420 to 600 when deterrnined by test method B producedby the process of claim 1.

17. A process for preparing a composition consisting of an active driedbakers yeast with a particle size of 0.1 to 1.0 mm and with a dry mattercontent of at least 85 percent by weight, a protein content N X 6.25)

of 45 to 60 percent on dry matter and an activity value of 420 to 600when determined by test method B consisting of the steps of dividing afresh compressed yeast having a protein content N X 6.25) of 45 to 60percent on dry weight basis into a mass of particles having across-section of 0.2 to 2.0 mm and drying the mass of particles in lessthan 20 minutes to a dry matter content of to percent by weight with aflow of drying gas passing through the mass at a temperature of not morethan C at the beginning and lower at the end of the drying periodwhereby the said particles are held within a range of 20 to 50C toobtain a dried bakers yeast.

1. A PROCESS FOR PREPARING A COMPOSITION CONSISTING ESSENTIALLY OF ANACTIVE DRIED BAKERS'' YEAST WITH A PARTICLE SIZE OF 0.1 TO 1.0 MM ANDWITH A DRY MATTER CONTENT OF AT LEAST 85 PERCENT BY WEIGHT, A PROTEINCONTENT (% N X 6.25) OF 45 TO 60 PERCENT BASED ON DRY TEST METHOD B2CONSISTING OF THE STEPS OF DIVIDDETERMINED BY TEST METHOD B2 CONSISTINGOF THE STEPS OF DIVIDING A FRESH COMPRESSED YEAST HAVING A PORTIONCONTENT (% N X 6.25) OF 45 TO 60 PERCENT ON DRY WEIGHT BASIS INTO A MASSOF PARTICLES HACING A PARTICLE SIZE OF 0.2 TO 2.0 MM AND DRYING THE MASSOF PARTICLES BY PASSING THERETHROUGH A DRYING GAS AT A TEMPERATURE OFNOT MORE THAN 160*C IN NOT MORE THAN 120 MINUTES TO A DRY MATTAR CONTENTOF AT LEAST 85 PERCENT BY WEIGHT WITH A DRYING GAS FLOW SO THAT THEPARTICLES ARE HELD WITHIN A TEMPERATURE RANGE OF FROM 20* TO 50*C TOOBTAIN A DRIED BAKERS'' YEAST.
 2. The process of claim 1 wherein thedrying time is less than 50 minutes.
 3. The process of claim 1 whereinthe drying time is less than 20 minutes.
 4. The process of claim 1wherein the temperature of the drying gas flow at the end of the dryingperiod is lower than in the beginning thereof.
 5. The process of claim 1wherein the yeast is subdivided by extrusion.
 6. The process of claim 1wherein the protein content (% N X 6.25) of the starting material is 48to 54 percent on dry weight basis.
 7. The process of claim 1 wherein theyeast is dried to a dry matter content of 90 to 95 percent by weight. 8.The process of claim 1 wherein the compressed yeast starting material ismixed with at least one member of the group consisting of swellingagents and wetting agents.
 9. The process of claim 8 wherein theswelling agent is methyl cellulose or carboxy methyl cellulose.
 10. Theprocess of claim 8 wherein the amount of swelling agent used is from 1to 2 percent based on dry matter.
 11. The process of claim 8 wherein thewetting agent is selected from the group consisting of an ester ofsaturated and unsaturated fatty acids, a fatty acid ester of glycerol, afatty acid ester of propylene glycol and mixtures of two or morethereof.
 12. The process of claim 8 wherein the amount of wetting agentused is from 1 to 2 percent based on dry matter.
 13. The process ofclaim 1 wherein yeast strain Ng 1777 is used as the starting material.14. The process of claim 1 wherein the compressed yeast startingmaterial used is prepared by partially dehydrating with a hypotonicsolution and quickly washing the solution from the yeast.
 15. Theprocess of claim 1 wherein the drying step is carried out continuously.16. In a process for making baked products from a dough containingyeast, the improvement which comprises using an active dried bakers''yeast with a dry matter content of at least 85 percent by weight, aprotein content (%N X 6.25) of 45 to 60 percent based on dry matter andan activity value of 420 to 600 when determined by test method B2produced by the process of claim
 1. 17. A process for preparing acomposition consisting of an active dried bakers'' yeast with a particlesize of 0.1 to 1.0 mm and with a dry matter content of at least 85percent by weight, a protein content (% N X 6.25) of 45 to 60 percent ondry matter and an activity value of 420 to 600 when determined by testmethod B2 consisting of the steps of dividing a fresh compressed yeasthaving a protein content (% N X 6.25) of 45 to 60 percent on dry weightbasis into a mass of particles having a cross-section of 0.2 to 2.0 mmand drying the mass of particles in less than 20 minutes to a dry mattercontent of 90 to 95 percent by weight with a flow of drying gas passingthrough the mass at a temperature of not more than 160*C at thebeginning and lower at the end of the drying period whereby the saidparticles are held within a range of 20* to 50*C to obtain a driedbakers'' yeast.